Usually, a brushless motor needs a detector for detecting the position of magnetic poles of a rotor of the motor. However, for example, in the case where it is difficult to use the pole position detector, there is employed a method in which the pole position detector is omitted and a commutation signal of the motor is generated on the basis of a voltage signal induced in an armature winding. This method will now be explained.
FIG. 1 is a diagram showing the construction of the conventional brushless motor operating apparatus. Reference numeral 1 designates a DC power source and numeral 2 designates a semiconductor switching element group which is composed of six transistors U to Z and six diodes connected in inverse parallel with the transistors. Numeral 3 designates a brushless motor which is composed of a three-phase connected armature winding 4 and a magnet rotor 5. Numeral 6 designates rotor position detection means which is composed of three filters 61 to 63 and a group 64 of comparators. Numeral 7 designates commutation signal generation means which performs a logical operation on rotor position detection signals 6U, 6V and 6W as outputs of the rotor position detection means to generate commutation signals 7U to 7Z of the transistors in the semiconductor switching element group 2.
With the above construction, in a rotor position detection operation mode in which a voltage signal induced in the armature winding 4 is detected and the brushless motor 3 is operated by a commutation signal generated on the basis of a rotor position detection signal obtained through conversion of the voltage signal by the rotor position detection means 6, the commutation signal generation means 7 receives rotor position detection signals 6U to 6W as shown in FIG. 2 and performs a logical operation thereon to generate commutation signals 7U to 7Z. The transistors in the semiconductor switching element group 2 are switched by those commutation signals, thereby causing the brushless motor to continuously generate a rotational torque.
On the other hand, during a time when the brushless motor 3 is stopped, no induced voltage is generated. Upon activation, therefore, commutation signals 7U to 7Z as shown in FIG. 2 are applied at a low frequency to forcibly rotate the brushless motor 3 at a low speed. By this rotation, induced voltages are generated in the armature winding 4. The induced voltages are converted by the rotor position detection means 6 to obtain rotor position detection signals 6U to 6W as shown in FIG. 2. The above operation mode is a synchronized operation mode. At the point of time when such rotor position detection signals have been settled in the synchronized operation mode, a signal source for the commutation signals 7U to 7Z is changed over to the rotor position detection signals 6U to 6W, thereby making transition to the rotor position detection operation mode.
In the above construction, there is well known a hard ware for the commutation signal generation means 7 which generates the commutation signals 7U to 7Z from the position detection signals 6U to 6W through the logical operation.
In the case where a microcomputer is used as the commutation signal generation means 7, there can be considered a method in which in the rotor position detection operation mode the microcomputer always monitors the rotor position detection signals 6U to 6W and generates the commutation signals 7U to 7Z in accordance with the (High or Low) levels of the rotor position detection signals. In this method, the monitoring of the levels of the rotor position detection signals is made even in the case where transition from the synchronized operation mode to the rotor position detection operation mode is made. Therefore, smooth transition is possible without specifically taking the timing of transition into consideration.
However, in the above method, the microcomputer must sample frequently the rotor position detection signals. Accordingly, the greater part of the control capacity of the microcomputer is used for the driving of the brushless motor and hence another control or a control for an equipment using the brushless motor is restricted.
Also, if the number of times of sampling is decreased in order to make the other control, an error in phase of the commutation signal is generated.
To solve the above problem in this method, there can be considered a method of taking to consideration the rise and fall edges of the rotor position detection signals. Namely, as shown in FIG. 3, the first to sixth patterns exist as output patterns of the commutation signals 7U to 7Z corresponding to the edge change-over of the rotor position detection signals 6U to 6W and these patterns are outputted in a sequence from the first pattern.
For example, when the rise of the rotor position detection signal 6U is detected at a timing a, commutation signals are outputted with the first pattern. Thereafter, when the edge of the rotor position detection signal 6W is detected at a timing b, the pattern of commutation signals is changed over to the second pattern. Subsequently, the edge of 6V, the rise of 6U, the edge of 6W and the edge of 6V occur at timings c, d, e and f, respectively, and the third to sixth patterns are sequentially outputted as the patterns of commutation signals, respectively. After the outputting of the sixth pattern, the first pattern is outputted again at the rise of 6U and the similar operation is repeated. In this method, it suffices that the microcomputer handles only the edges of the rotor position detection signals as interruption signals. The microcomputer can make another control during the other time. Therefore, the utility efficiency of the microcomputer is greatly improved.
In the above method, however, since the edges of the rotor position detection signals 6U to 6W and the sequence of the commutation signals 7U to 7Z are uniquely determined, the smooth driving of the motor is not possible unless the output sequence of the first to sixth patterns is strictly kept. Especially, there is a problem that if the rotor position detection signals and the commutation signals are linked in a proper sequence at a timing of transition from the synchronized operation mode to the rotor position detection operation mode, smooth transition is impossible.